This invention relates to comminutors, and more particularly to an impact rotor assembly for reducing large diameter wood products and stumps to size.
Impact crushers for the reduction and classification of ore utilizing an impact rotor to obtain the initial reduction of large ore chunks are known in the prior art. See U.S. Pat. No. 3,887,141 to P. M. Francis. Francis discloses a mill in a single housing. A primary reduction chamber located within the housing is fed raw ore with variable particle sizes up to and including chunks on the order of 1 foot in diameter. An impact rotor is positioned within the primary reduction chamber and secured to the output shaft of a drive motor. The impact rotor mounts a plurality of elongated hammer bars around its periphery. These hammer bars are oriented parallel to the rotational axis of the impact rotor. The rotor is positioned so that the ore, falling under the influence of gravity, is directed against the hammer bars and repelled therefrom with great force against the sides of the primary reduction chamber.
Application of Francis-type pulverizing mills to wood waste is also known. See U.S. Pat. No. 4,151,959 to C. L. Deister. The Deister patent discloses an impact pulverizer having a rotor located concentrically within a reduction chamber. The rotor has a plurality of generally radially-extending impact blades. The radial angle of the blades increases along the axis of the rotor to provide each of the blades with a slope in the axial direction of the rotor. The spiral rotational action of the pieces as they are propelled and ricocheted around the primary reduction chamber achieves a faster pulverizing action than Francis-type pulverizing mills. The spiral rotational action also requires less power that the Francis mill.
Prior art pulverizing mills are ineffective in reducing logs because the wood is not hard enough to shatter, i.e., the resiliency of wood requires a shearing and grinding effect. Although neither the Francis nor the Deister mills are able to reduce wood logs to size, the principal of the spiral Deister rotor has been applied to a rotary wood hog for reducing logs. Rawlings Construction Co. of Montana, markets a rotary wood hog which uses a helical rotor to reduce elongated wood products to size. By use of an anvil at the front of the rotary hog, the Rawlings helical rotor is able to shear and grind pieces of the log during each revolution of the rotor.
The increasing radial angle of the Rawlings rotor blades attempts to move the material being acted upon in a generally spiral rotational motion. Because logs are generally most efficiently fed into a rotary wood hog at lengths of ten feet or more and in a direction where a log's longitudinal axis is parallel to the rotor's radial axis, the spiraling action of the rotor blades will move the end of the log being acted upon by the rotor toward one corner the reduction chamber. The log being reduced will thereby tend to change from an upright vertical position to a horizontal position frequently causing a bridging-type jam when the length of the log matches the width of the rotor housing, i.e., the log will bridge the rotor and block additional material from reaching the rotor blades. This is especially a problem when dealing with larger diameter wood products, i.e., 24 inches to 40 inches because of the extensive shut down required to remove the jammed pieces which are large and heavy. Even without jamming, uneven wear of the rotor blades will take place.